xfs: Don't wake xfsbufd when idle

The xfsbufd wakes every xfsbufd_centisecs (once per second by
default) for each filesystem even when the filesystem is idle.  If
the xfsbufd has nothing to do, put it into a long term sleep and
only wake it up when there is work pending (i.e. dirty buffers to
flush soon). This will make laptop power misers happy.

Signed-off-by: Dave Chinner <david@fromorbit.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>

diff --git a/fs/xfs/linux-2.6/xfs_buf.c b/fs/xfs/linux-2.6/xfs_buf.c
index 77b8be81c76900559d8e382ee9e7a42710ae86e5..18ae3ba8f78ab78af240cb8f2bc9ad4e147636e4 100644 (file)
--- a/fs/xfs/linux-2.6/xfs_buf.c
+++ b/fs/xfs/linux-2.6/xfs_buf.c
@@ -1595,6 +1595,11 @@ xfs_buf_delwri_queue(
                list_del(&bp->b_list);
        }
 
+       if (list_empty(dwq)) {
+               /* start xfsbufd as it is about to have something to do */
+               wake_up_process(bp->b_target->bt_task);
+       }
+
        bp->b_flags |= _XBF_DELWRI_Q;
        list_add_tail(&bp->b_list, dwq);
        bp->b_queuetime = jiffies;
@@ -1644,6 +1649,8 @@ xfsbufd_wakeup(
        list_for_each_entry(btp, &xfs_buftarg_list, bt_list) {
                if (test_bit(XBT_FORCE_SLEEP, &btp->bt_flags))
                        continue;
+               if (list_empty(&btp->bt_delwrite_queue))
+                       continue;
                set_bit(XBT_FORCE_FLUSH, &btp->bt_flags);
                wake_up_process(btp->bt_task);
        }
@@ -1708,6 +1715,9 @@ xfsbufd(
        set_freezable();
 
        do {
+               long    age = xfs_buf_age_centisecs * msecs_to_jiffies(10);
+               long    tout = xfs_buf_timer_centisecs * msecs_to_jiffies(10);
+
                if (unlikely(freezing(current))) {
                        set_bit(XBT_FORCE_SLEEP, &target->bt_flags);
                        refrigerator();
@@ -1715,12 +1725,12 @@ xfsbufd(
                        clear_bit(XBT_FORCE_SLEEP, &target->bt_flags);
                }
 
-               schedule_timeout_interruptible(
-                       xfs_buf_timer_centisecs * msecs_to_jiffies(10));
-
-               xfs_buf_delwri_split(target, &tmp,
-                               xfs_buf_age_centisecs * msecs_to_jiffies(10));
+               /* sleep for a long time if there is nothing to do. */
+               if (list_empty(&target->bt_delwrite_queue))
+                       tout = MAX_SCHEDULE_TIMEOUT;
+               schedule_timeout_interruptible(tout);
 
+               xfs_buf_delwri_split(target, &tmp, age);
                count = 0;
                while (!list_empty(&tmp)) {
                        bp = list_entry(tmp.next, xfs_buf_t, b_list);